In many industrial processes having multiple circulating fluid paths it is often necessary to have selective mixing of the fluids in the fluid paths. As such, a valve assembly is often positioned between two fluid paths that can be selectively articulated to permit or prevent mixing of the fluids circulating in the fluid paths. A commonly employed valve assembly for controlling the flow of fluids between two circulating fluid paths is a double seat valve assembly.
A double seat valve generally comprises two flaps each mounted to a movable body that can be independently moved to open or close an orifice between the circulating fluid paths. In most double seat valve assemblies, the movable body to which one of the flaps is mounted is hollow and defines a leakage path for selectively draining either fluid path. In this configuration, the two sets of flaps can be selectively engaged to each other to restrict the flow of fluid into the leakage path. The flaps of the double seat valve are can be generally configured in three operational modes. In the first mode, both sets of flaps are engaged to each other and the orifice to prevent flow of fluid between the two fluid paths and into the leakage path. In the second mode, both sets of flaps are engaged to each other, but are disengaged from the orifice to allow the flow of fluid between the two fluid paths while preventing the flow of fluid into to the leakage path. In the third mode, the first flap engages the orifice to prevent flow of fluid between the two fluid paths while the second flap is disengaged from the first flap and the orifice to allow flow of fluid from one of the fluid paths into the leakage path. The third operation mode is often used for selectively flushing of one of the fluid paths with cleaning or flushing fluids that are immediately discharged into the leakage path.
Double seat valves provide significant flexibility by allowing selective control of the flow of fluid between multiple fluid paths and allowing independent flushing of one of the fluid paths. However, double seat valves are inherently complex to provide all the required features with multiple moving parts that must be moved both independently and in unison. As such, the implementation and maintenance costs of double seat valves can be significant.
A related drawback is that sets of flaps must be effectively sealed to both the orifice and each other requiring seals to be employed, particularly to insure an effective seal between the flaps. An ineffective seal can cause inadvertent mixing of drainage of the fluids from the fluid paths, which can lead to significant problems when one of the fluid paths is being selectively cleaned with harsh cleaning chemicals while the other fluid path contains a product fluid such a liquid-food.
An approach to preventing cross-contamination of the fluid paths is disclosed in US Patent Application 2009/0008594 and is directed to an annular protrusion in the orifice for directing the fluid in the fluid path to be flushed to the center of the leakage path. Correspondingly, a spout is formed on the flap sealing the orifice during flushing adapted to interface with the protrusion. This approach significantly complicates the manufacturing process of the valve assembly. Another approach to prevent cross-contamination of the fluid paths is disclosed in US Patent Application 2009/0065077 and is directed to a barrier element between the flaps to protect the flap sealing the orifice. Specifically, the barrier element deflects the stream of flushing fluid from the flap sealing the orifice. However, the barrier element only accounts for one cause of leakage between the fluid paths. Both of the above references are herein incorporated by reference in their entirety.
As such there is a need for a means of effectively sealing the orifice during flushing situations that can account turbulent flow at the flaps, the pressures on both sides of the sealing flap, the types of fluids involved on both sides of the sealing flap and the positions of the relative components of the valve.